1. Field of the Invention
This invention relates to a method for washing a tank and recovering and treating residual tank liquid and, more particularly to such a method for discharging and recovering residual liquid remaining in an oil tank and for, as appropriate, conducting various tank treatments such as discharge and removal of sludge remaining in the tank by breakdown and dissolution with jetted oil, final washing with cold or hot water, and oil-water separation of discharged liquid.
2. Description of the Prior Art
The usual method used for removing the waxy sludge that accumulates in oil tanks is to break down and dissolve the sludge by spraying it with high-pressure liquid from a liquid jetting device and to discharge the dissolved sludge and the jetted liquid out of the tank.
After the interior of the tank has been washed with oil or the like in this manner, the oil film adhering to the inner surface of the tank has to be removed by final washing with cold or hot water so as to make it safe for entry by the maintenance personnel for inspection and repairs.
Various equipment is required for carrying out this washing operation, including a high-pressure oil supply device, a hot water supply device, a suction device for sucking and discharging residual tank liquid, an oil-water separator for separating oil from the discharged residual liquid, a filter treatment device for treating the separated oil and an inert gas supply device for supplying an inert gas into the tank for fire and explosion prevention during tank washing, all of which have to be installed in the vicinity of the oil tank to be treated. The installation of this equipment is very time consuming and costly. The equipment also takes up a considerable amount of space around the tank being treated.
Up to now, therefore, the washing of an oil tank has been an extremely expensive, large-scale operation that has required the tank to be taken out of operation for a long period of time.
The present invention was accomplished in light of the foregoing circumstances and has as one object to provide a system and a method for washing a tank and recovering and treating residual tank liquid.
Another object of the invention is to provide such a system and method that employ a closed system wherein liquid and gas recovered from the tank are returned to the tank for reuse so as to reduce discharge of liquid and gas to the exterior.